In recent years the pressure for production of increased oil and gas has led to increased use of wells drilled at angles with respect to the vertical. This is done for a variety of reasons, for example, to effect a wide area of coverage from a single well head, such as an off-shore oil platform. Other reasons for drilling at angles include avoiding drilling through large upthrusts of material located directly over formations of interest, and avoiding having to drill through corrosive material such as found in salt domes. The art recognizes that there are other applications of drilling at angles to the vertical as well.
The typical well drilling procedure, particularly in exploration for oil, gas and other minerals involves the rotation of a drill bit at the end of a long tubular drill string. A drilling fluid or "mud" is pumped down the center of the drill string, to exit around the hollow drill bit, and carries the cuttings drilled from the subsurface formation back to the surface for removal. The mud also provides a cooling effect to the drill head. In a well drilled along the vertical the cuttings are carried to the surface by the mud passing around the drill head on all sides. However, in a well drilled at an angle to the vertical, the tendency is for the mud to flow upwardly along the upper side of the drill string because it is typically of lower density than the metallic drill string. The absence of a mud current on the lower side of the drill string allows a bed of cuttings to build up under the drill string. This can be a severe problem in some cases because the cuttings bed can build up to such an extent that the drill string is distorted and forced into the upper side of the wall of the well. Another problem occurs when one tries to remove the drill head, which is typically of larger diameter than the drill string; the cuttings bed built-up behind the drill head prevents or impedes its removal.
Numerous expedients have been suggested for ensuring that cuttings are removed properly from a well drilled at an angle to the vertical and some of these are successful. However, one area which the art has not addressed is the provision of a method for determining whether the cuttings are, in fact being properly removed from a well, so as to determine whether any of these methods should be used, and, if they are used, whether or not they are working effectively.